Photomechanical processes



D. c; GRESHAM PHOTOMECHANICAL PROCESSES Julie 21, 1955" Fildua 12, 1952 2 Sheets-Sheet 1 NEGATIVE IMAGE m POSITIVE IMAGE" uuuseo E MULSl ON DYE AND REHALO- m SILVER (HALIDEJSUBSEQUENTLY GENIZED SILVER v FIXED our) 0= DENSITY.

GLASS OR FILM SUPPORT IN VENI'OR.

DONALD .CHARLES GRESHAM" AT TORNEYS JuneiZl, 1955 I Filed May 12,. 1952 II I r I 1 BLUE-SENSITIVE, FINE LINE ILENS I PHOTOGRAPHIC 9 f & ELEMENT E I I ExPosING NEGATIVE I3A PROCESSING NEGATIVE (a) YELLOW COLOR I DEVELOPMENT (b) WASH (cyaLEAcI-I sILvER (a WASH AND DRAIN {I I BLUE-SENSITIVE |WH|TE cARD INTRODUCED LENS I I ELEMENT 4I FOR PART OF {a I I I BEARING YELLOW ll EXPOSURE "l2 I NEGATIVE L I I LINE IMAGE REVERSAL POSITIVE EXPOSURE I38.

sILvE D. c. GRESHAM l 2,711,372

IPHOT OMECHANICAL PROCESSES I 2 sheets-sheet 2-.

fPRocEssING POSITIVE ,(a)DEvEI oP TO sI vER DYE NEGATIVE IMAGE v D I (b) FIX TO REMOVE uNusED J HALIDE AND ALSO I A REHALOGENIZED E I POS'TWE NEGATIVE SILVER v I (c) WASH 1 I (d)DlSSOLVE 0 BLEACH INVENTOR; DONALD' CHARLES G EsHAM ATTORNEYS United States Patent f PHOTOMECHANICAL PROCESSES Donald Charles Gresham, London, England, assignor to McCorquodale 8; Company Limited, London,-England, a British company Application May 12, 1952, Serial No. 237,419

Claims priority, application Great Britain September-'7, 1951 3 Claims. (Cl. 95-5) This invention relates to photomechanicalprocesses and particularly to the production of records of discontinuous tone subjects and is an improvement in or modification of my Patent No. 2,704,252 filed th January, 1951.

In Patent No. 2,704,252 I have described inter alia a new method of producing positives directly from originals by a reversal technique, which method comprises exposing a photographic plate or film to light. from an original subject, developing to silver thelatent image obtained, thereby producing a negative image in silver, producing a coloured image in situ therewith and bleach.- ing the said silver image, exposing the said plate or film to light incident on the same side thereof as the'original exposure, the said light being of a colourto which the.

photographic emulsion is sensitive but which is absorbed by the said coloured image, redeveloping the 'said plate or film, fixing the plate or film to remove any residual silver halide, and removing the coloured image. The coloured image may be formed by dye-toning or mornegative area of the plate or film duringthe-second,

danting but in the'preferred formfof the invention the first development is effected by me ans of an aromatic primary amino compound in the presence of a colour 5f former which couples with the oxidation products of the developer to form a dyestufi' image.

. By the said process a positive image in silver is directly.

obtained. Owing to the fact that the dyestutf negative image absorbs the re-exposure light the silver halide lying.

below the dyestufl? image is not re-exposed. Accordingly it is not necessary to go to the length of full fiIStf6X-- posure and commercial variations in emulsionsthickness have no effect on the result obtained. Generally speak.- ing it is suflicient to use photographic f'platesior films which are not optically sensitised, ie.'which have only their natural sensitivity toblue light. With suchplates and films it is preferred that the colour former should be one'which yields a yellow or yellow-orange image- The colour former may be included inthe original'photo graphic emulsion ormay be included in the developer used for the first development only. Generally speak ous negative areas ing the second development will be effected by means'of A wide range of colour formers is .idescribedfl-in the literature and examples of:colour formers suitable for the present invention maybe selected from the list ,of yellow-orange colour formers set out in theBritish Journal of Photography, volume 85, p. 648.

It is, of course, important thatthe agent selected for use in bleaching the initially'formednegative silverimag'e should be one which does not adversely affect the residual silver'halide or the dyestuti image. A suitable bleach of line originals;

asdin the conventional ggp'roduct is laterally correct for litho printing-and soob fthe drawings;

I 'i a tenteddune 25; 15955 ing agent consists'of an aqueous solution of potassium= ferricyanide and potassium bromide. ln order that no image should be developed in the developmentstageit isimportant that all thesilver halide rendered developable in 'the first exposure shoul-dbe (k1. ,veloped inthe first development. This can usually'be achieved by prolonging the'first development stepfb'ut, as an alternative the first developmentnean be completed by treating the plate or film in a'vigo r'ousdeveloper, erg.

ametol-hydroquinone type of developer.f"The developer used for the second development stage, producing the positive image, is preferably one giving a highcontr'ast image and caustic soda-hydroquinone developers have been found very useful. "-It is advantageousl to include a small quantity of'an anti-fogging agent'in second developenfe. g. benzotriaz ole orany' other of the well known heterociyclic compounds having anti f'ogging action 7 when included in developers.

The removal of the dye imageis usually efrected as a1 final'stage in the preparation of the screen positive. Gen-. 'erally speaking, the quinone-imine or azomethine dyes;

. produced by colour developers, using colour formers of 1 relatively simple structure;aresoluble inficommon or-5 1, ganic solvents" and one convenient method of removing l the dye image therefore is to ofirnethyl alcohol, acetone andglacialiacetic acid;

, As stated in application "Serial No; 206,120 the fore going method is especially suitable for the reproductionllt' affords results'as goodpas are ob I tained by the usual negative-positive process and has. the additional advantage. that only-a normal negative ex poj sure is required instead "of a greatly'increas'ed exposure reversal process. Moreover the viates the use of a'prism on the camera.

Irithefdrawing: 1 Fig.1 (A is-a etfect'obtained by the process just described.

Fig. 1(B) is a diagra'mmaticalillustration illustrating the process of the present invention.

ofthe presentinvention';

5 "The e'ifect obtained .by-the'aioiresaid process is diagramrnaticallyiillu'strated' in the' accompanying Fig. 1(A) of (i! haloge f izedlf The areas betweenithediscontinuare exposed bythe'se'condexposure and the silvershalide lying below the said negativeareas 1 It :will further be observed from the drawing that, the result is indefpendent of errnilsion thiokis not rewexposed.

ness. 'Ihe emulsion haspbee'n illustrated vvith an;exagger- .atedrvarlationin thickness but'the: areas of the'discontinuousimage obtained.'isl 'independent of this variation.

The ordinary reversalprocess, however, in whichthe wholeiof the silverhalidefwhich was unused in thefirst so "that the final lt has beenfound 'however thatwhere the process is apphed'to the reproductionof line originals ofsu'ch-characterv dry-po nt etchings, Where'the-original contrast is exposure is exposed in thefsecond exposure is essentially.

dependent on emulsion; thickness variations. The line AA'on this drawing illustrates diagrammatically the: ef-: feet of a' uniform second exposure. It will lee-understood a V diagrammatic and that the depth, of. the imagej jareas' 'representsnot so much their that the" drawingjisiflpurely physical depth buttheirIeffective density.

veryj'low and' 'moreover the finest lines are usually of very'low'density and the closely hatched shadow areas tend to. be more orjlessvblocked-up, the quality of the bathe the plate or filmin f an organic solvent medium for the dyestuif. I LA suitable-j medium for many colour-formed dyestufis'isa mixture, I

-diagrammatical illustration jshowing lthe FigfZ is afiow sheet illustrating the 'steps in th' e process.

Itwill be observed thatftheinegative image -1s formed in dye-and silver-and the latter "is bleached reproduction obtained is still not all that could be desired. This is also the case where the original is itself a screen image.

Such originals may generally be described as finedetail discontinuous tone originals. According to the present invention a method of producing positives directly from fine detail discontinuous tone originals by a reversal technique comprises exposing a photographic plate or film to light from such original subject, developing to silver the latent image obtained, thereby producing an image in silver, producing a coloured image in situ therewith and bleaching the said silver image, exposing the said plate or film to light incident on the same side thereof as the original exposure, the said light being of a colour to which the photographic emulsion is sensitive but which is absorbed by the said coloured image, the second exposure being efi'ected at least partially to light from the original subject, redeveloping the said plate or film, fixing the plate or film to remove any residual silver halide and removing the coloured image. Since the highlights of the original subject reflect most light and the shadows least light the effective re-exposure of the plate or film is greatest in the highlights and least in the shadows, which results in a correction of the gradation while providing the correct tonal range.

In practice it has been found that the relative intensities of the highlights and shadows of the original subject are usually such that, if the whole re-exposure is effected to the original subject an over-correction results. Accordingly in the preferred form of the invention, part of the re-exposure is effected to the original subject, sufficient to effect the desired tonal correction, and the remainder of the re-exposure is effected to uniform light. The optimum ratio of these exposures depends on the photographic material and the method of plate making employed but is generally found to be of the order of to :1.

The effect obtained is diagrammatically illustrated in Fig. 1(3) of the drawings. This figure is similar to Fig. 1(A) but the line BB is shown drawn at an angle to represent the efiect of a second exposure which is modulated image wise by the original. The effect of this is greatest in the regions corresponding to those regions of the original which have the least area of black detail and, as shown, allows the negative to be made with sufiicient exposure to record detail adequately in closely hatched areas of the original. Such exposure would normally be excessive for adequate recording of the fine detail in open areas of the original particularly if, as is often the case, such detail has low density.

In carrying out this form of the invention the plate or film, after first development, is replaced, either in wet or dry condition, in the process camera and registered in its original position so that the second recorded image is exactly in register with the first recorded image. An exposure sufiicient to effect the desired tone-correction is then eiiected and thereafter the original is covered with a sheet of white reflecting material and the exposure continued until the required total re-exposure is reached. Both parts of the re-exposure are, of course, effected via an appropriate filter selected to transmit only light of wavebands absorbed by the negative dye image (which may be associated with the re-halogenised silver).

A flow sheet of this method is illustrated in Fig. 2. Referring to this drawing a fine line original 11 is copied in the camera (illustrated as lens 12) on to a photographic element 13A. The element 13A is color developed, washed, treated to bleach the silver image, washed, drained, and (now identified as 133) replaced in the camera in its original position. The second exposure is made partially to original 11 and partly to a white card 14. The element 135 is then processed to develop a silver image, to remove residual silver halide and bleach negative silver, washed and treated to remove the dye image. This gives the final product 13C which ill 4 carries a silver fine line position which records faithfully both fine isolated black detail and closely hatched dark areas of the original.

The following example will serve to illustrate the invention.

Example A camera with a process lens of 18 inch focal length was used and the illumination consisted of four 30 amp. open-arc lamps at 3 /2 feet from the centre of the copyboard.

A dry-point etching was set up on the camera as the original. The scale of reproduction was X 0.7, requiring a camera extension of 740 mm.

1. A Kodak B5 Process Slow plate was placed in the camera and an exposure of 22 seconds was given to the original through a tri-colour blue filter (Wratten 49-- the word Wratten being a registered trade-mark) at a lens aperture of 11.5 mm.

2. The plate was developed for 7 /2 minutes at F. in a yellow-forming colour developer constituted of equal parts of the following solutions A and B.

A. N.N-diethyl-p-phenylene diamine, sulphur dioxide reaction product g 4.5 Sodium sulphite (anhydrous) g 18. Potassium bromide g 4 Water to make 2250 cc.

B. Acetone cc 200 2.5-dichloracetoacetanilide g 20 Sodium hydroxide g 14 Sodium carbonate (anhydrous) ..g 132 Water to make 2250 cc.

3. The plate was washed for 2 minutes.

4. The plate was bleached for 5 minutes in a solution of 50 g. potassium ferricyanide and 50 g. potassium bromide in a litre of water.

5. The plate was washed for 10 minutes.

6. The plate was replaced in the camera in precisely the same position as it occupied for the first exposure.

7. The plate was re-exposed to the original subject, without a filter for 210 seconds, the lens being at full aperture (46 mm.). cred with white paper and a further exposure given of 10 seconds at a lens aperture of 27 mm.

8. The plate was then developed for 4 minutes at 65 F.

in a developer made up of equal parts of the following solutions A, B and C.

A. Hydroquinone g 38 Potassium metabisulphite -g 38 Potassium bromide "g. 19 Water to make 2 litres.

B. Potassium hydroxide g Water to make 2 litres.

C. 1% solution of benzotriazole ..cc 45 Water to make 2 litres.

value of about 3.0 on an average batch of the sensitive material specified but on any batch of the material the gamma value will be at least approximately 2.5 as will be appreciated by those skilled in the art. The conditions of second development given in the example will yield a gamma value of about 5.0 on an average batch of the sensitive material specified but on a batch of the materialthe gamma value will be at least approximately 4.0.

In accordance with a further aspect of the present The original subject was then covinvention line originals are reproduced by printing down in register a line positive of the original madeby the process of the invention and a screen positive of the original made by the process of application Serial No. 206,120. Thus for example a line positive may be made by the process set out in the foregoingsexample and a screen positive of the same subject may be made by the process of Example 2 of application Serial No. 206,120. By printing these positives down onto metal and printing the line positive record in black and the screen positive record in grey, a reproduction of the original subject of remarkably high fidelity is obtained.

It is sometimes desirable to make a screen positive by enlargement from small screen images. This is particularly useful for posters which may be larger than .the largest screen available but where a coarsescreen image resulting from the enlargement is not'a, disadvantage.

The usual procedure is to.make a normal screennegative and to rephotograph the trans-illuminated negative in the" camera without the screen and at the required magnificav tion. This usually results in a screen positive with excessive contrast and poor tonal gradation; The process of the present invention provides a definite solution to this problem. The preferred method is as follows:

A screen positive is made from a continuous tone original, retouched and proofed. The screen positive is preferably made by the method described in application Serial No. 206,120 but any screen positive which gives asatisfactory proof can be used. The screen positive is set up in the transparency holder of the camera and is photographed on a photographic element of inherently high contrast characteristics, at the required magnification. The photographic element is developed in a colour developer and the silver is rehalogenised in a ferricyanidebromide bath. The photographic .element is then re placed in the camera in the position it occupied for the first exposure and is given an exposure to the original A verysmall amount of difi'usion may usefully be introduced screen positive followed by a uniform exposure.

during the exposure to the original screen positive, for

fixing out:the undeveloped which. does not appreciably "afiect the dye image, bleaching the silver image'in thetbleaching bath to be'used, measuring the densities" of the wedge steps through a filter of complementaryicolor to the dyeimage, plotting these densities against the logarithms of the exposures T which produced them and deriving the "gradient value from the curve in the usual way.

" Iclaimp l. A method of producing positives directlyjfrom fine" detail discontinuous tone originals'by a reversal {technique which method comprisesexposing a photographic element having an emulsion of high contrast to light' froml j such originalsubject, developing the fine line latent image thus obtained with an aromatic primaryamino develop-'- ing agentin the presence'of a eolor'coupler-fwhich com bines' with the oxidationproducts of such developer .to

producela dye image, therebysproducing a negative image made up ofareas of developed'silverwith a dye image.

in situ therewith, said development bein g suchas to pro- I duce a dye image with a gamma value'or" at least approxi mately 215, bleaching the said silverimage, exposing the I, ,j

unexposed arleasfofthe said element to light incident on.

the same side thereof as the original exposure, thesaid' light being era color to which the photographic emulsion is sensitive andbe'ing of such color and intensity that the light is substantially; completely absorbed by thebsaid colored image, the second exposure being 'eiiected atleast partially to light from the original 'subject,-redev elopin'g the said element to a gamma of at 'least approximately i 4.0 in a developer which will notredevelop any rehaloa, genized silver negative image'which may be present, fixing' the element to remove'the residual siiverhalide remaining f below the negative image whichlias beenopticailyj screened from thesecond exposure, any 'silverhalide'r'emaining below thepositive image and anyrehalogenized 1 silver of the negative imagejwh'ich may be .presentpandt;

,tlien removing the negative dye'image;.

instance by placing a sheet of matt plastic in contact with the camera side of the original screen positive. These exposures must be by light of a colour to which the plate is sensitive but to which the dye image has high density.

Finally the photographic element is developed in a high contrast developer, fixed and the dye is removed. By

suitably adjusting theratio of uniform exposure to imagewise exposure it is possible to obtain an exact reproducj tion of the tone value of the original screen'positive and,

since the original positive has been proofed, the result which will be obtained from the enlarged positive may procedure for colour-separation screen positives -mad e from the original. p

t-will be noted that in the foregoing example the photographic material specified has an emulsion with .high contrast and when this expression is used in-the appended claims it has reference to one of the many commercially available materials made primarily for the production of linear screen records. At the present time these fall into classes which I define as follows: (a) Materialsiwhich,

when exposed to White light and developed for 3 minutes at 68 F. in Kodak developer D11, yield a gamma value 7 3 of at least 3.5; (b) materials of the Kodalithf type which have silver chloride" emulsions and when developed'in special developers containing formaldehyde or reaction;

products of formaldehydeyield a'gamma value. of at least 4.0.

When I refer to a gamma value of a dye image I refer to a figure derived by developing a step Wedge on the" material to be used in the color developer to be used,

I ence ofacolor coupler which combines with [the oxida tion products of suchfdeveloperftoproducea'dyeimage, thereby producing arne gative image made "upfof areasofideveloped silver with a dyeimage in si tu therewith,."said 2. A method ofproducing positives di1ectlyfr om finet line originals by a reversal technique which-method comprises exposing aphotographic elementhztying an emulsion of high contrast to light'from such: original subject}. developingthe' fine line-latent irnage thuspbtained'with; e

an aromaticprimary amino developing agent in the pres development. being such as to produce adye, image-with a gammasvalue of at least approximately 2.5 bleachingthef V -saidsilver image, exp osirigthefunexposedfirbaS ofthe said element to lightiincidentorithe same sidefthereof as the original XPO ure, the said light being' of a colorfto' whichjthe photographic. emulsion is sensitive and being of such. color and intensity thattheglight is substantially" completely absorbed by thesaid-colored image, 'thtse'cond 3 exposure being effected at :the original subject, :re

least partially .to light from sion of high contrast to. lightfrom suchorigihalfsubject; I developing the fine line j latent imageI thus obtained with an aromatic primary aminodeveloping'agent'inthe presonce of a'color coupler which combines with'the oxidation productsof s'uichldeveloper to produce' adye image "thereQ. I by producinga'ne'gative image made of areas, of devel oped silver with a'dye image infsitu theiewithjfsaid"development being such as to producea dye image with n gamma value of atleast.approximately,2.5,;bleaching' the said silver image exposing the unexposed areas of p i silver halidehin a-j fixingbath v ev'eloping the said element; to.-;a gamma of at leastappr'gxiniately ,4;O- in; a- 'developer j whi'ch'will not'redevelop any rehalogeniied silver-negative l image which may be present, fixingthe element'to rerriove I l 1 any residual silverhalideandremoving the colored image; i

3. method of producing positives directly i from'finei line 'originalsby a reversal technique whichini'ethodcom i prises exposing a photographic element having ian ertttllsaid element to light incident on the same side thereof as the original exposure, the said light being of a color to which the photographic emulsion is sensitive and being of such color and intensity that the light is substantially completely absorbed by the said colored image, the second exposure being effected partly to light from the original subject and partly to uniform light, the ratio of these parts being 15 to 30:1, redeveloping the said element to a gamma value of at least approximately 4.0 in a developer which will not redevelop any rehalogenized silver negative image which may be present, fixing the element to remove any residual silver halide and removing the colored image.

References Cited in the file of this patent UNITED STATES PATENTS 2,165,407 Murray July 11, 1939 2,182,814 Marasco Dec. 12, 1939 2,327,822 Russell et al 2 Aug. 24, 1943 FOREIGN PATENTS 593,839 Germany Mar. 6, 1934 OTHER REFERENCES Process Engraver's Monthly, February 1947, page 50; August 1948, pp. 236-237; September 1948, pp. 287-288. 

1. A METHOD OF PRODUCING POSITIVES DIRECTLY FROM FINE DETAIL DISCONTINUOUS TONE ORIGINALS BY A REVERSAL TECHNIQUE WHICH METHOD COMPRISES EXPOSING A PHOTOGRAPHIC ELEMENT HAVING AN EMULSION OF HIGH CONTRAST TO LIGHT FROM SUCH ORIGINAL SUBJECT, DEVELOPING THE FINE LINE LATENT IMAGE THUS OBTAINED WITH AN AROMATIC PRIMARY AMINO DEVELOPING AGENT IN THE PRESENCE OF A COLOR COUPLER WHICH COMBINES WITH THE OXIDATION PRODUCTS OF SUCH DEVELOPER TO PRODUCE A DYE IMAGE, THEREBY PRODUCING A NEGATIVE IMAGE MADE UP OF AREAS OF DEVELOPED SILVER WITH A DYE IMAGE IN SITU THEREWITH, SAID DEVELOPMENT BEING SUCH AS TO PRODUCE A DYE IMAGE WITH A GAMMA VALUE OF AT LEAST APPROXIMATELY 2.5, BLEACHING THE SAID SILVER IMAGE, EXPOSING THE UNEXPECTED AREAS OF THE SAID ELEMENT TO LIGHT INCIDENT ON THE SAME SIDE THEREOF AS THE ORIGINAL EXPOSURE, THE SAID LIGHT BEING OF A COLOR TO WHICH THE PHOTOGRAPHIC EMULSION IS SENSITIVE AND BEING OF SUCH COLOR AND INTENSITY THAT THE LIGHT IS SUBSTANTIALLY COMPLETELY ABSORBED BY SAID COLOR IMAGE, THE SECOND EXPOSURE BEING EFFECTED AT LEAST PARTIALLY TO LIGHT FROM THE ORIGINAL SUBJECT, REDEVELOPING THE SAID ELEMENT TO A GAMMA OF AT LEAST APPROXIMATELY 4.0 IN A DEVELOPER WHICH WILL NOT REDEVELOP ANY REHALOGENIZED SILVER NEGATIVE WHICH MAY BE PRESENT, FIXING THE ELEMENT TO REMOVE THE RESIDUAL SILVER HALIDE REMAINING BELOW THE NEGATIVE IMAGE WHICH HAS BEEN OPTICALLY SCREENED FROM THE SECOND EXPOSURE, ANY SILVER HALIDE REMAINING BELOW THE POSITIVE IMAGE AND ANY REHALOGENIZED SILVER OF THE NEGATIVE WHICH MAY BE PRESENT, AND THEN REMOVING THE NEGATIVE DYE IMAGE. 